Differential bracket issues Superformance early Mod. 100's

[Moto Guru]

Deleted post

[eschaider]

Originally Posted by Moto Guru

I was able to pry out the metal from the frame that holds up the front differential. As you can see from the metal close-ups the material is very frail.

I am uncertain how to visually measure the "frailty" of any metal. Can you explain the process?

Originally Posted by Moto Guru

The actual alloy was bad on this one,

That may be. Please tell us more about the chemistry of the alloy steel that failed and what it should have been. Please elaborate a bit on what elements you found in the steel and what elements were missing. If there were no elements missing please advise us the actual concentrations of the elements you found in the steel vs the correct concentrations that you believe should have been present.

Originally Posted by Moto Guru

and was missing some welding.

How did you determine there was missing welding? Did you compare the component to another SPF Cobra or perhaps did you have manufacturing documentation that called out for a different type or location of weld?

Originally Posted by Moto Guru

I'll keep looking at this thread to see if anyone can give me pointers.

Please read post #10 and post #12. They will give you excellent guidance on improving the diff mounting in the chassis.

Originally Posted by Moto Guru

The passenger side bracket is a PAIN to get to especially taking out the top bolt, there is almost no room to work at all. I'm talking fingertips here.

These bodies are fiberglass. You should have no difficulty getting at the top of the location to weld. Just cut a hole in the fiberglass floor above where you want to weld. Remove the now liberated piece of fiberglass. Clean the surface to be welded. Position the pieces you wish to weld. Go in with your TIG torch weld what every you would like to weld. After cool down, clean the surface for painting. Paint the surface to prevent rusting. Re-glass the piece of flooring you just cut out. Paint it to look pretty and you are done!

Originally Posted by Moto Guru

Take a look at the metal, looks like there was a bad heat sink or bad cast when they made or heat-treated this particular metal. Something doesn't look right.

I have an SPF and I have never found a heat sink anywhere on the chassis. In the picture you posted I also do not see a heat sink.

If you mean that you think the heat treatment is incorrect you probably ought to know the steel used in that section of the chassis (and I think everywhere else) is not heat treated it is almost certainly condition "N" steel, possibly condition "A" steel but likely condition "N" steel.

In your determination of heat treat status what type of test did you use to determine the heat treatment?

In the FWIW category the piece of damaged mounting hardware you displayed in the photograph looks as if the mounts were not tight. The freedom of movement the loose mounts afforded the nose of the differential housing, allowed the differential nose mounting hardware to hammer against the mount eventually tearing the mild steel. This would have taken some time to accomplish.

Just looking at your photo it would appear the damaged component approximates 0.125" in thickness. That thickness of mild steel, in a properly designed mounting, should be more than adequate to restrain the nose of the IRS housing.

All that being said, if you want to very securely mount the IRS center section to your chassis the solution / answer is in post #12 above.


Ed

[twobjshelbys]

Originally Posted by eschaider

I am uncertain how to visually measure the "frailty" of any metal. Can you explain the process?




That may be. Please tell us more about the chemistry of the alloy steel that failed and what it should have been. Please elaborate a bit on what elements you found in the steel and what elements were missing. If there were no elements missing please advise us the actual concentrations of the elements you found in the steel vs the correct concentrations that you believe should have been present.




How did you determine there was missing welding? Did you compare the component to another SPF Cobra or perhaps did you have manufacturing documentation that called out for a different type or location of weld?





Please read post #10 and post #12. They will give you excellent guidance on improving the diff mounting in the chassis.




These bodies are fiberglass. You should have no difficulty getting at the top of the location to weld. Just cut a hole in the fiberglass floor above where you want to weld. Remove the now liberated piece of fiberglass. Clean the surface to be welded. Position the pieces you wish to weld. Go in with your TIG torch weld what every you would like to weld. After cool down, clean the surface for painting. Paint the surface to prevent rusting. Re-glass the piece of flooring you just cut out. Paint it to look pretty and you are done!





I have an SPF and I have never found a heat sink anywhere on the chassis. In the picture you posted I also do not see a heat sink.

If you mean that you think the heat treatment is incorrect you probably ought to know the steel used in that section of the chassis (and I think everywhere else) is not heat treated it is almost certainly condition "N" steel, possibly condition "A" steel but likely condition "N" steel.

In your determination of heat treat status what type of test did you use to determine the heat treatment?

In the FWIW category the piece of damaged mounting hardware you displayed in the photograph looks as if the mounts were not tight. The freedom of movement the loose mounts afforded the nose of the differential housing, allowed the differential nose mounting hardware to hammer against the mount eventually tearing the mild steel. This would have taken some time to accomplish.

Just looking at your photo it would appear the damaged component approximates 0.125" in thickness. That thickness of mild steel, in a properly designed mounting, should be more than adequate to restrain the nose of the IRS housing.

All that being said, if you want to very securely mount the IRS center section to your chassis the solution / answer is in post #12 above.


Ed

I think first I'd like an explanation of how almost 900hp was not the major contributing factor. This sounds like a case of pilot error to me.

[eschaider]

Originally Posted by twobjshelbys

I think first I'd like an explanation of how almost 900hp was not the major contributing factor. This sounds like a case of pilot error to me.

I would normally agree, Tony, except the OP indicates he is extracting that power from a 354" naturally aspirated small block. The numbers work out to essentially 2.5 hp per cubic inch. While not ProStock power levels (3 hp per cubic inch) it is close enough to raise the question of, "it it real or is it memorex" to steal a line from years gone by.

I suspect the represented engine power level is an optimistic wish with no dyno paperwork to support it. The real world power is probably closer to 550 FWHP, likely less, that will work out to about 450-ish at the tire — best case.

The real problem is a maintenance issue not a power, chassis design or strength of materials issue. Someone abused the car and when they heard the clunking in the back continued to beat on it until it failed. Once failure arrived the blame game begins. There are enough of us with SPF replicas that make more power, more torque and do not seem to suffer these sorts of failures. It is an abusive operation / lack of maintenance type failure — nothing more and nothing less.

My questioning was just to point out that the OP was sprouting potential problems like a popcorn machine at a movie theater without any knowledge of what he was talking about - let alone testing to provide some sort of basis for the representations.


Ed

[Moto Guru]

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